ttest returns NaN even though matrices are finite and does not contain nan?

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Sugyani Mahapatra 2017-8-30

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https://ww2.mathworks.cn/matlabcentral/answers/354626-ttest-returns-nan-even-though-matrices-are-finite-and-does-not-contain-nan

编辑： Adam Danz 2019-12-10

I have 2 matrices: sample1 - 17*80 and sample2 - 17*80

find(isnan(sample1)==1) and find(isnan(sample2)==1) are empty matrices.

Similarly, find(isfinite(sample1)==0) and find(isfinite(sample2)==0) are empty matrices.

[h,p] = ttest(sample1, sample2) results into a 1*80 vector, each value = NaN.

Why does it happen so??

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Katerina Merculy 2018-4-13

I have the same problem and vextors are not the same, they even have different number of rows and I compare ttest(mean(sample1),mean(sample2)) Have you decided this question?

Stephen23 2018-4-13

@Katerina Merculy: please upload your data in a .mat file.

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Answer 1

Anthony Peng 2017-9-19

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https://ww2.mathworks.cn/matlabcentral/answers/354626-ttest-returns-nan-even-though-matrices-are-finite-and-does-not-contain-nan#answer_282277

Are the two vectors the same? If they have the same values in them, it will return NaN.

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ANKUSH JAMTHIKAR 2019-12-10

I have two binary vectors with same elements. I mean, if X and Y are the two binary vectors, then X=Y. Now when I am running ttest(X,Y), it is giving me h=NaN and p=NaN. Does anyone know, how to handel this issue?

I am a bigginner in statistics. So kindly help me to understand this.

Thank you in advanced!

Adam Danz 2019-12-10

编辑：Adam Danz 2019-12-10

@Katerina Merculy, you're getting NaN values because mean(sample1) and mean(sample2) result in scalar values which is interpretted as a 1-sample ttest (not a paired ttest) and you need at least 2 values to carry out the test. Instead of inputting the mean, input the raw values.

@ANKUSH JAMTHIKAR, when the x and y inputs to ttest(x,y) are exactly equal, you should expect a NaN results.

For more detail on both problems, see this answer which explains in detail why NaN results occur in ttest().

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